Currently, when a lithium ion battery is used under 20˜40 degrees, the charge and discharge performance of the lithium ion battery is generally the best, and the life is the best. When the battery is in a low temperature environment, it needs to make the temperature of the battery go back to the best working temperature range by means of the heating function of thermal management. While, it usually adopts two heating methods, i.e. external PTC heating and hot air heating, to heat the battery in the market.
Referring to FIG. 1, the external PTC heating is that a heat exchanger 9 for flowing through the liquid is integrated in a battery pack P, while the liquid in a tank 7 is pumped by a pump 10, heated by a PTC heater 8 and then enters into the heat exchanger 9, so that heat exchange is performed between each mono-battery 1 of the battery module M and the liquid working medium. Along the flowing direction, the liquid working medium transfers the heat continuously to each mono-battery 1 of the battery module M in the path, thus the temperature of the liquid working medium decreases gradually, and the capability of transferring heat decreases gradually. Therefore, each mono-battery 1 of the battery module M in the flowing path receives the different quantity of heat, the longer the flowing path is, the bigger the difference of the temperature between each other is. Thus, the mono-battery 1 of the battery module M at the end of the flowing path receives the minimum heat, and the rising speed of temperature is the slowest, which affects the heating efficiency of the whole module. In addition, due to the endothermic effect of piping components and the heat loss of pipe wall exposed to the circumstance, a very large part of heat cannot be used by the battery module in the PTC heating, and the effective utilization of heat is low.
Referring to FIG. 2, the hot air heating is that hot air produced by a hot air heater A is pumped into the battery pack P by a blower B of the battery pack P, thereby improving an internal environment temperature of the battery pack P and heating each mono-battery 1 of the battery module M. Due to air as the medium, such a heating way is easily implemented, but the efficiency of heating is lower, and an IP level of a battery pack case C is low. Alternatively, the hot air heater is integrated into the battery pack case C, but the space occupied by the hot air heater A is large, the integration degree of product is poor, which is not beneficial to market the product, at the same time the battery pack case C needs a relatively bigger space to optimize a flow duct of air, so as to improve uniformity of the temperature of the battery, which results in the space utilization of the battery pack P low.
As can be seen from the two modes of heating, the existing problems and defects of the prior art is: heat is transmitted through the fluid, the structure is complex, many components are related, and the demand of space is big; the heat has a large loss and the effective utilization of heat is low during heat transmission; because it is difficult to control the heat loss along the flowing path of the fluid as desired, so the wooden barrel short board effect of heating function is obvious; the difference of the temperature of the heated object is large and is difficult to control.